Impact of Habitat Quality on Mule Deer Reproduction and Survival
In the 1990s, mule deer populations began to decline across the western United States. CPW researchers set out to identify reasons for the decline, focusing on those factors that could be controlled through management efforts. Researchers recognized both habitat quality and predation as possible factors, but did not know which one played a larger role in mule deer population declines.
To evaluate habitat as a limiting factor, researchers measured the effect of habitat enhancements on mule deer survival and fawn recruitment during a six-year study.
During the winter months, researchers artificially enhanced habitat quality by distributing feed supplement pellets around the study area to improve deer nutrition. Predation levels were left unchanged. Researchers then measured pregnancy rates, doe body condition, and doe and fawn survival rates in the supplemented area and in an un-supplemented control area. Halfway through the study, the treatment and control areas were reversed in a crossover design.
Fawn survival in the supplemented area was significantly greater than in the control area during the winter, which resulted in a positive rate of population increase. These results provided clear evidence that nutrition and habitat quality were important factors contributing to deer population declines.
This CPW project aligned with a research project conducted by the Idaho Fish and Game Department, which found that predator control had a smaller positive effect on declining mule deer populations.
Although completed in 2005, this project still serves as a reference and basis for many of CPW's current research projects. This project also helped wildlife managers determine factors that could be managed to reverse mule deer population declines.